The present invention relates generally to the non-contact repair of microelectronic circuits and in particular, to the repair of flat panel displays, such as active matrix liquid crystal display panels.
During the manufacturing of liquid crystal (LC) displays, large clear plates of thin glass are used as a substrate for the deposition of thin film transistor (TFT) arrays. Usually, several independent TFT arrays are contained within one glass substrate plate and are often referred to as TFT panels. Alternatively, an active matrix LCD, or AMLCD, covers the class of displays utilizing a transistor or diode at every subpixel, and therefore encompasses TFT devices. Such glass substrate plates may also be referred to as AMLCD panels. Flat panel displays (FPD) may also be fabricated using any of the organic light-emitting diode (OLED) technologies and though typically fabricated on glass, may also be fabricated on plastic substrate plates.
TFT pattern deposition is performed in a multitude of stages where in each stage, a particular material (such as a metal, indium tin oxide (ITO), crystalline silicon, amorphous silicon, etc.) is deposited on top of a previous layer (or glass) in conformity with a predetermined pattern. Each stage typically includes a number of steps such as deposition, masking, etching, stripping, etc.
During each of these stages and at various steps within each stage, many production defects may occur that may affect the electrical and/or optical performance of the final LCD product. Such defects include but are not limited to metal protrusion 110 into ITO 112, ITO protrusion 114 into metal 116, a so-called mouse bite 118, an open circuit 120, a short 122 in a transistor 124, and a foreign particle 126, as shown in FIG. 1. Other defects include mask problems, over or under etching, etc.
Even though the TFT deposition processes are tightly controlled, defect occurrence is unavoidable. This limits the product yield and adversely affects production costs. Typically, the TFT arrays are inspected using one or multiple automated optical inspection (AOI) system(s) following critical deposition stages and by an opto-electrical inspection machine, also referred to as array tester or array checker (AC) to test the finished TFT arrays. Usually AOI and AC systems provide defect coordinates; they do not provide high resolution images required to classify defects as killer defects, reparable defects, or imperfections that do not affect TFT array performance (also known as process defects). The defect coordinate information from AOI or test systems is passed to a TFT array review/repair tool, also referred to as array saver (AS), in which defects are reviewed, classified, and then repaired.
The average number of defects per plate may vary (a) depending on the maturity of the fabrication process, (b) from one TFT array manufacturer to another and (c) from one manufacturing plant to another. Typically, the defect review and repair capacity within the TFT array fabrication line is sized to process 300-400 defects per Generation 7 plate (2100 mm by 2400 mm in size. Typically 5 to 10% of defects per plate require repair.
Since the TFT array features are typically very small (sub-pixel size may be, for example, 80 by 240 micrometers and up to 216×648 micrometers for large 40 inch LCD televisions made from Generation 7 plates), the array review/repair tool includes a microscope to perform a defect review to decide whether the defect is repairable. The microscope field of view is small (ranging from 100×100 μm to 2×2 mm) relative to the plate size (typically 2.1×2.4 m). The microscope is installed on a precision XY stage so that it can be dispatched from one defect to another over the plate surface. The defect coordinates are known from inspections carried out earlier by AOI and AC inspection systems. The glass plate remains stationary under the XY stage by means of a vacuum chuck during the defect review and subsequent repair. The reviewed defects are classified, or binned, into various categories, including those requiring repair. The repairable defects are further binned by specific repair types, typically laser machining or cutting (also known as “zapping”), laser welding, or bridging an open line.
The above series of general events is typical of all array review/repair tools. The number, type, locations, size/degree of defects often vary from plate to plate and a means to pass judgment is required at almost all of the tool steps following capture of the defect images—for example, whether an image is truly a defect rather than nuisance, what kind of defect has been found, whether or not a specific defect needs repair, what kind of repair is required, what repair parameters are needed, what is the next defect to be repaired, and so forth. Some review/repair tools combine tool operation with human operator judgment and intervention to identify, classify, and then repair such defects. Other review/repair tools, such as the ASx60 family of review/repair tools manufactured by Photon Dynamics, Inc., include an automatic defect repair (ADR) capability that automatically, i.e. without human intervention, analyzes review and AOI/test data, identifies and classifies defects, and then sets up the repair parameters, and executes the repairs.
FIGS. 2 and 3 show two defect repair examples in cross sections. Metal protrusion defect 110 is shown in FIG. 2A (see FIG. 1 for top view). In this example, after identifying and classifying the defect 110, a repair recipe is created, and then executed to remove the protrusion, as shown in FIG. 2B. Material removal is a relatively straightforward process, using laser cutting techniques to control position and power/size parameters of the laser beam.
FIGS. 3A-3E represent the repair steps performed to correct an open path between metal lines 32 and 34. In this example, a laser 36 is used to break through (“zap”) the passivation layer 38 to expose or cut into the metal lines. Then, a means to deposit material, a chemical vapor gas and moving laser energy source in this example, is introduced to create contact electrodes 42 and 44 on the metal lines 32 and 34. Thereafter a metal line 46 is formed to connect the two metal lines 32 and 34.
Compared to repairs requiring cutting such as shown in FIG. 2, repairs requiring correction of open paths such as shown in FIG. 3 are far more challenging, because new material must be introduced to correct such defects. Challenges include material integrity and compatibility, such as, adhesion, resistivity, continuity, line width, line thickness, etc., of the new material with the panel, accuracy of placement (plate circuit features and defects within them are typically less than 1 to 10 micrometer), and speed of application as the deposition process to repair a single open defect should take well less than tens of seconds, and so forth. Typical repair line-widths are less than 10 micrometers and lengths on the order of 100 micrometers, and the desired material deposition time per repair is on the order of seconds. In a production line, it is desirable to review and then repair defects within the same tool. A suitably selected direct write or printing approach can meet these challenges. “Direct write” is any technique for creating a pattern directly on a substrate, either by adding or removing material from the substrate, without the use of a mask or pre-existing form. Typically, direct write techniques may employ lasers or particle beams (for example, electron beams) that have beam diameters on the order of the desired repair line widths, and that are controlled with CAD/CAM programs. Direct write deposition methods include, for example, ink jet printing, laser chemical vapor deposition (LCVD), and other methods, some of which are described below.
Laser Direct Write Deposition Methods:
Laser chemical vapor deposition (LCVD) is a well known technique for open line repair of flat panel displays. It uses a laser beam focused on the surface of a substrate to induce localized chemical reactions. Often the substrate is coated with a precursor, which is either pyrolyzed or photolyzed locally where the laser beam scans. Pyrolytic laser CVD is roughly the same as thermal CVD. In photolytic CVD, a chemical reaction is induced by the interaction between the laser light and the precursors. FIGS. 3C and 3D represent the photolytic LCVD process. LCVD requires controlled atmospheres, specifically, a balance of precursor gas flows with vacuum, and hence, LCVD equipment includes gas flow controllers, valving, vacuum pumps, and other plumbing.
LCVD shortcomings include: (i) slow deposition rates (on the order of, for example, many tens of seconds for 3500 Angstrom thick, 5 micrometer wide by 100 micrometer long lines), (ii) requirement for controlled environment surrounding the area to be repaired; specifically, any gases near the repair must be purged and then inert gases or vacuum must be introduced to avoid contamination, (iii) requirement for preparation of surfaces prior to deposition for best adhesion, (iv) requirement for elevated surface temperature for best adhesion, (v) high complexity of manufacturing equipment, and (vi) potential to introduce contamination because of gas flows near the substrate.
Currently, the LCVD process is slow and its associated tools are expensive, and FP production lines typically include a number of lower cost review/cutting repair tools, such as the ASx60 products manufactured by Photon Dynamics, Inc., and a separate LCVD tool dedicated for line open repairs. FIG. 19B illustrates the current typical flow of FP plates through the sequence of review/repair tools in a production line.
Laser induced forward transfer (LIFT) methods for deposition of relatively small features were introduced in the 1980s. In the LIFT method, a pulsed laser beam is directed through a laser-transparent target to strike and vaporize a film of material to be transferred that coats the target substrate on the side opposite the laser beam. LIFT is a homogenous pyrolytic technique because the laser vaporizes the film material. Laser energy densities for LIFT metal transfer cited by Mayer (U.S. Pat. No. 4,752,455) are in the range of 1 to 10 J/cm2. Vaporized material tends to be more reactive and more easily degraded, oxidized or contaminated. The LIFT method is not suitable for organic materials because it is a high temperature method. Further, since high temperatures are achieved at the target material, ablation or sputtering of the target substrate itself may also occur, resulting in transfer of the target substrate material which reduces the integrity of the purity of the desired film material. There have been reports that lines created by the LIFT process have poor uniformity, morphology, adhesion and resolution.
Micro-structuring by explosive laser deposition (MELD) is a variant of LIFT and is described by Mayer in U.S. Pat. Nos. 4,752,455 and 6,159,832. Mayer uses very short pulses (less than or equal to 20 psec) at very high repetition rates (10 MHz) at energies per pulse of 10 mJ. The laser beam passes through a transparent substrate whose opposite surface is metallized. The beam vaporizes the metal film material and propels it toward the target substrate. The typical energy density is approximately 1 to 3 J/cm2. The '832 patent describes the use of ultrafast lasers. The laser metal transfer (LMT) process under development by Omron Corporation (Japan) is closest to the MELD work of Mayer. Since both LIFT and MELD require the vaporization and condensation of a metal film on the surface of a substrate, the functionality (i.e. electrical conductivity) of the resulting patterns is marginal since the material exhibits numerous discontinuities between adjacent voxels (or transferred 3-dimensional pixels).
Ink deposition via painting, brushing, jetting has been a path of interest for direct write of electronic circuits since the mid-1990s using lasers with narrow beams and nano-inks (with metal particles on the order of five to many tens of nanometers in size). The United States Department of Defense's Defense Advanced Research Projects Agency (DARPA) Mesoscopic Integrated Conformal Electronics (MICE) program from about 1999 to 2002 funded several direct write technology approaches, with target line widths in the mesoscopic range (1 to 100 micrometers).
Aerosol jet is a method of application of ink material to a substrate developed by Optomec, Inc., Albuquerque, N. Mex., under the DARPA MICE program. In this method, the delivery system includes (1) an atomizer that breaks the ink into a distribution of droplets of 1 to 10 micrometer diameter, with a mean of approximately 5 micrometer, and (2) a delivery head that includes a sheath gas jet concentrically placed around the ink stream. The concentrically placed gas focuses the ink stream. The deposited ink line must then be cured. Current techniques employ a wide distribution of droplet sizes. The technology seems to be most successful in direct write deposition of metal lines greater than 20 micrometers, and has found application in fabrication of three dimensional structures well above the 100 micrometer size. However, shortcomings of this approach to achieve lines less than 10 micrometer in width include: (i) highly complex process dependencies (for example, ink temperature, ink viscosity, atomizer pressure and temperature, gas sheath flow), (ii) frequent clogging of delivery needle, (iii) mean of droplet distribution limited to approximately 5 micrometer, which limits line width minimum to approximately 7 micrometer, (iv) limited to materials having viscosities less than about 1000 cP; and (v) factors determining linewidth include mean of droplet distribution, ink viscosity, ink/substrate surface tension, temperature.
The application of printer inkjet technologies for direct write deposition of microcircuits continues to be explored. Inkjet printhead droplet-on-demand dispensing technologies using piezoelectric, thermal, electrostatic, acoustic, or other drives have been well documented. Production-level applications typically dispense droplets in the tens of picoliter volume or more. Ten picoliters is equivalent to approximately a 26 micrometer diameter sphere. For repair of microcircuits found in flat panel displays, however, line widths of less than 10 micrometers are required. If some allowance for spreading of the deposited ink is included, droplets of diameter 4 micrometers may satisfy FP repair requirements, and such droplet sizes are equivalent to tens of femtoliters of volume. Though developments continue, inkjet technologies for very fine line widths have not yet been proven for production. Many of the same limitations listed above for aerosol jet technology apply to the print-on-demand inkjet technologies.
The matrix-assisted pulsed laser evaporation direct-write (MAPLE-DW) was developed under DARPA's MICE program by Chrisey and Pique of the U.S. Naval Research Laboratory. The MAPLE-DW approach is described by U.S. Pat. No. 6,177,151 (the '151 patent) and U.S. Pat. No. 6,766,764 (the '764 patent). Several subsequent variations of MAPLE-DW are described by U.S. Pat. Nos. 6,805,918 (the '918 patent) and 7,014,885 (transfer of rheological materials) (the '885 patent), and U.S. Pat. No. 6,815,015 (jetting behavior) (the '015 patent). U.S. Pat. Nos. 7,014,885 and 6,815,015 are incorporated herein by reference in their entirety. The MAPLE-DW process is a variant of LIFT, and the key distinction between the two is that in LIFT, the material to be transferred is ablated or vaporized, and therefore substantially changed during the transfer due to the high energy applied, while in MAPLE-DW the transferred material is substantially unchanged.
The key differences amongst the three variants (MAPLE-DW, rheological, and jetting) lie primarily in (a) the nature of the material to be transferred, (b) the laser energy density, and (c) the transfer mechanics which depends on both the nature of material and available energy. The MAPLE-DW process describes combining a transfer material with a matrix material, which specifically has the property of being more volatile than the transfer material when exposed to pulsed laser energy. The transfer materials may include but not be limited to metals or non-metals including insulators as well as biological materials. The coated material (matrix plus transfer materials) is assumed to be in solid state during the deposition process. Transfer energy densities for metals using the MAPLE-DW process are cited in '151 and '764 as typically 300 to 500 mJ/cm2. The MAPLE-DW transfer mechanism consists of volatizing or vaporizing the matrix material, which then causes desorption of the transfer material from the supporting ribbon to the receiving substrate. The MAPLE-DW process assumes that after transfer, the deposited material needs no additional processing.
The rheological material and process is described in the '918 and '885 patents, which define rheological materials as the class of material with properties that lie in a range between solid and liquid, and are characterized by at least one fundamental rheological property such as elasticity or viscosity. Further, the rheological materials include but are not limited to gels, pastes, inks, concentrated solutions, suspensions, Newtonian and non-Newtonian fluids, viscoelastic solids and elastiviscous fluids. The rheological materials may include but not be limited to metal or non-metal including insulators as well as biological materials. The rheological materials are homogeneous mixtures comprised of (for example) functional materials, solvent or vehicle, chemical and rheology precursors, binders, surfactants, dispersant agents, powders, and/or biomaterials. The functional material is the material that contains the functional properties (such as electrical, magnetic, and so forth) of the desired deposit. Transfer energy densities for metals using the rheological material transfer process were cited in the '918 patent examples as 400 to 500 mJ/cm2. The rheological material transfer mechanism as described by the '918 and '885 patents consists of the following steps: (a) the laser energy locally heats a very small volume of the rheological fluid near the supporting ribbon surface, and then (b) the vaporized material generates a high pressure burst that propels the non-vaporized fluid forward to the receiving substrate. The material that is transferred is substantially unchanged rheological fluid. Most deposition materials require post-processing such as thermal, photothermal, or photolytic processes to decompose any chemical precursors, or drive off solvent vehicles, or consolidate or density or sinter the functional materials and permanent binders.
The jetting effect described in the '015 patent occurs under narrow process window conditions using rheological fluids. Specifically, the transfer energy density is tailored to control the transfer process so that the material transferred remains roughly the same size or smaller than the incident laser beam profile. Transfer energy density for the jetting process reported in the '015 patent is less than 100 mJ/cm2. Operation in the jetting window is advantageous in that feature sizes comparable to the incident laser beam size may be created. More specifically, such feature sizes may be in the range less than 10 micrometers, which is the requirement for repair of FP open line defects. However, the conditions for jetting behavior as described in the '015 patent requires relatively thick coatings (1 to 20 micrometers thick, and more specifically 5 to 10 micrometers in the cited example) on the transparent ribbon, which result in equally thick transferred features, far larger than the sub-micron thickness required in FP repair.
Of highest interest for the FP industry are the processes that support ink or rheological materials because deposition repairs may require non-metals, for example, photoresist materials or organic-based materials used in color filters, as well as conductive materials, for example, metals. However, as noted already, typical minimum feature sizes required for FP repair are 5 micrometer wide by typically 0.2 to 0.4 micrometer thick lines with relatively small edge roughness, on the order of a few tenths micrometer. Most of the direct write techniques described above can easily achieve 30 micrometer line widths, and with some additional but modest effort, 10 micrometer line widths. Except for LCVD, other ink-based DW techniques, for example, jetting, cannot routinely achieve uniform and continuous sub-micron line thicknesses.
Limitations to achieving 5 micrometer wide by 0.3 micrometer thick lines with good edge roughness using ink/rheological materials include, for example, (i) material flow at the receiving substrate surface, which can be a function of delivery or substrate temperature, viscosity, substrate material or surface conditions, (ii) delivered droplet size (aerosol jet or ink jet) or delivered material size and thickness (material transfer methods), (iii) relative position of the delivery mechanism to the receiving substrate. In the case of an ink jet system, for example, too large a distance may result in too wide a line (spread of jet) while too close a distance may also result in too wide a line (splatter of the jet). Additional limitations to achieving 5 micrometer wide lines with good edge roughness using ink/rheological materials include: (iv) material particle size in the ink or rheological material, for metals, typical metal particles sizes should be in tens of nanometers or less, (v) aperture size in delivery mechanisms, and (vi) beam size of the laser or energy source.
The materials to be transferred in the LIFT and MAPLE-DW processes are usually solids, whereas the rheological materials are homogeneous mixtures including functional material, solvent or carrier materials, binders, dispersants and so forth, any of which contribute to the rheological properties such as viscosity. Some selected rheological materials may include solvents or fluids with low, but non-zero, vapor pressures, which implies potential change in the rheological material over time due to evaporation of such solvents or fluids. Thus, for consistent results, particularly at line widths less than or equal to 5 micrometers, a requirement is that the rheological material to be transferred have consistent properties over time. Ensuring this requirement may be achieved in several ways: (a) place the rheological material to be transferred within an environment that inhibits change (for example, control temperature and pressure conditions), or (b) control the sequencing of process and handling steps such that the rheological material's exposure time at transfer is always the same.
Duignan et al in U.S. Pat. Nos. 6,792,326, 6,583,318, 6,82,490, 6,85,426, and 6,649,861 reference describe an apparatus for MAPLE-DW. Duignan's apparatus cannot be applied to laser direct write methods using rheological materials for a number of reasons such as (a) Duignan does not accommodate the requirement for maintaining consistent rheological material properties over time, (b) Duingan does not provide for the requirement for post-processing for the purposes of driving away the carrier components within the rheological fluid, etc.
Thus, there is a need for an apparatus and methods that enable repeatable deposition repairs using the rheological materials and associated process steps.
The NRL team and Duignan et al. describe apparatus and methods combining laser direct write deposition with laser machining (zapping), and both groups describe machining for preparation of the receiving substrate prior to deposition and machining or trimming of the resulting deposition. In the '918, '885, and '015 patents, the NRL team introduces the requirement for post processing (curing). Addiego in U.S. Pat. No. 5,164,565 combines a laser machining (cutting) repair function with a deposition repair function, but does not include the critical review function required for FP production.
As described already and noted in FIG. 19B, the current production flow of flat panels through a production line uses two kinds of tools to cover all types of FP repairs: (i) a review/cutting repair combined tool and (ii) a stand-alone deposition repair tool. Thus, there is a need for a low cost, fast defect review/repair tool that combines the review and all repair functions, and more specifically, automatically reviews and classifies defects, and then produces and executes instructions for cutting repairs and deposition repairs (such as those using rheological materials) while the panel of interest remains loaded within the tool.